(Invited) Stress Evolution on the Solid Electrolyte in Lower Temperature Operating Planar Sodium Nickel Chloride Batteries

Abstract

Sodium nickel chloride (Na-NiCl2) battery is one of the most promising candidates as a large scale electrochemical energy storage device since it offers high safety, long lifetime, and high energy density. The battery comprises molten metallic Na and NiCl2 as negative and positive electrodes, respectively, separating them by a β”-Al2O3–family solid electrolyte (BASE). In order to facilitate fast sodium-ion transport in the cathode compartment, the battery typically operates at 300oC accompanying with molten NaAlCl4 (catholyte), which is infiltrated into the cathode materials powder. A drawback of the efficient battery hampering broader market penetration is high manufacturing cost as it adopts expensive heterogeneous sealing technologies, such as thermal compression bonding, glass sealing, and laser beam welding, which are inevitable to withstand its high operating temperature. However, when lowering the operating temperature down to below 200oC, inexpensive polymer can be introduced replacing all the expensive sealing technologies, through which cell manufacturing process can be substantially simplified at the same time.In developing the lower temperature operating planar Na-NiCl2 battery, one of the major cell failure modes is mechanical failure in solid electrolytes either by thermal stress accumulation upon freeze-thaw cycles or by stresses developed by pressure difference between cathode and anode compartments during charge-discharge cycles. The presentation will start with defining failure modes of this new class of Na beta-alumina battery with special emphasis on electrolyte failure. In order to understand the stress accumulation in the vicinity of the solid electrolyte, a set of finite element analyses (FEA) has been conducted for various simulated conditions. It turns out that (1) sealing temperature, and (2) inner volumes of cathode and anode compartments need to be carefully designed to avoid the mechanical failure. The results of the calculation and cell design strategy for this novel battery will be discussed. Figure 1